Current limiting in the windings of electromagnetic devices



y 1960 R. o. DECKER ET AL 2,937,321

CURRENT LIMITING IN THE WINDINGS OF ELECTROMAGNETIC DEVICES Filed July12, 1957 WITNESSES INVENTORS ,6 Richard Q Decker a a W wo rmr Leonhard$17 WW M6,

ATTORNEY CURRENT LIMITING IN THE WINDINGS OF ELECTROMAGNETIC DEVICESRichard 0. Decker, Murrysville, and Werner Leonhard, Edgewood, Pa.,assignors to Westinghouse Electric Corporation, East Pittsburgh, Pa., acorporation of Pennsylvania Application July 12, 1957, Serial No.671,599

Claims. or. 317-156) Our invention relates to an electromagnetic controlsystem, and, more particularly, toa system for limiting the current inthe winding, or coil, of an electromagnetic device designed to beenergized with alternating current but in use is being supplied with adirect current, or 'at least one having a large direct-currentcomponent.

The coil of a solenoid operated valve, solenoid actuated clutch,designed to be normally operated from a source of alternating current,or the coil of an alternating-current contactor, each represents animpedance highly dependentonthe position of the armature, or othermovable part with reference to the other parts of the magnetic circuitinvolved. In a contactor, for example, in open conditions the impedanceis small, but the impedance increases rapidly as the armature moves fromits unactuated position to its fully actuated position. That is, theimpedance increases with a decrease of the air gap in the magneticcircuit with the inductance being a maximum when the air gap is closed.When such a device is operated from a stiff alternating-current voltagesource, the contactor takes a high current surge which produces enoughforce to pull the contactor in even though the air gap is large. As soonas the air gap closes, the impedance increases rapidly and inconsequence the current is reduced to a safe value, sufiicient to holdthe contactor in.

This inherent current limiting characteristic which allows an economicaldesign, is the distinguishing feature between alternating-current anddirect-current contactors.

With the extensive use of magnetic amplifiers in control circuits,having half wave rectified direct current output alternating-currentcontactors are'at times connected in the output circuit of the magneticamplifier. If an alternating-current coil is thus energized from amagnetic amplifier, namely, a magnetic amplifier having a half-wavedirect-current output, then the coil has to be redesigned, which isimpractical, or some other means have to be provided, as currentlimiting resistors cut in by extra relays or auxiliary contacts on thecontactor.

One broad object of our invention is the provision of static means forlimiting the current in an inductive load when energized with a directcurrent.

Another broad object of our invention is the provision of controllingthe output of a magnetic amplifier supplying an inductive load as afunction of the impedance of the load.

These objects here stated are merely illustrative. Other objects andadvantages will become more apparent from a study of the followingspecification, ing drawing, in which:

Figure 1 is a diagrammatic showing of the simplest embodiment of ourinvention; and

Figure 2 is a somewhat more elaborate diagrammatic showing of ourinvention.

In Fig. 1, a generally conventional alternating-current contactor, ACC,is shown connected in the output circuit of a substantially conventionalhalf-wave magnetic amplifier MAI.

This invention is, however, not restricted in use to the and theaccompany.

- in control winding 7 2,937,321 Patented May 17, 1960 shown. Themagnetic circuit carries the control windings- 9 and 14 and the mainwinding 2. The main winding 2 is connected in a circuit that may betraced from the lefthand terminal 1 of a suitable source of single-phasealternating current, main winding 2, rectifier 3, poled as indicated,conductor 4, armature actuating winding 5, conductor 6 to the right-handterminal 7 of the alternatingcurrent supply.

The control winding 14 is connected in a circuit fromalternating-current terminal 12, rectifier 13, poled as indicated,control winding 14 to the alternating-current terminal 15. Thealternating currents supplied to terminals 1 and 7, and 12 and 15 are inphase with instant polarities as shown. The voltage on terminals 12 and15 may be made variable, may be arranged to have a directcurrentcomponent of a selected value, or be of a direct current character of aselected value. Usually in this circuit, voltage between terminals 12and 15 is a resetting voltage that is opposed by a control signal.arrangement, when there is no control signal, the voltage betweenterminals 12 and 15 resets the core during its resetting half cycle,which half cycle is the half cycle when terminal 12 is positive and whenterminal 15 is negative, and during the following gating half cycle,when the polarities at terminal 12 and 15 are as shown in Fig. 1,substantially no current fiows in the output circuit, namely, thecircuit including the coil, or actuating winding 5.

When a control signal is present, the voltage between terminals 12 and15 is opposed during the resetting half cycle. The control signal must,of course, be of sufiicient magnitude to block the rectifier 13 duringthe resetting half cycle. Therefore, no flux reset occurs and a heavycurrent will flow in coil 5 which half cycle is a gating half cycle. Onthe immediately subsequent resetting half cycle some current will flowin the circuit from conductor 6, through conductor 8, device 50 whenused, conductor as indicated, to conductor 4. This current in controlwind ing 9 will be small in comparison to the current that flows 9 insubsequent resetting half cycles after the contactor ACC pulls in. Afterthe contactor ACC pulls in, a relatively heavy current flows in controlwinding 9 during the resetting half cycles. The reason for the currentflow in winding 9 during the resetting half cycles is because of theinductive nature of the coil 5. The current in winding 9 thus increasesas the contactor pulls in. The winding relation of the control winding 9with respect to the windings 2 and 14 is such that the ampere turnsincrease the resetting of the core of the magnetic amplifier MAI. Thisincreased resetting reduces the output of the gating cycles. Since themagnitude of the current in coil 9 is here directly related to theposition of the armature with respect to the stationary portion of themagnetic circuit, it is apparent we have provided a reliable,dependable, and self-adjusting current limiting For this during the nexthalf cycle,

10, rectifier 11 poled 3 The contactor ACC is interconnected with amagnetic amplifier MA2 such that the feed-back circuit in parallel withcoil 5 includes conductor 8, device 50 when used, control winding 9 onmagnetic amplifier MA2, rectifier 11, poled as indicated, to conductor4. The magnetic 5 amplifier MA2 is also provided with a control winding33. in the adjustable voltage circuit including negative terminal 31,adjustable resistor 32, control, or bias, winding 33, and conductor 34to the positive terminal 35.

A more positive feed-back signal than obtained with 1 the circuit shownin Fig. I, can be obtained with the circuit arrangement shown in Fig. 2.The magnetic amplifier MA3 has main, or output, windings 41, and controlwindings 42 and 43. Winding 42 is the feedback winding receiving itssignal from magnetic amplifier MA2. Here magnetic amplifier MA3 servesas a preamplifier for magnetic amplifier MAI. The polarities indicatedin Fig. 2 for the terminals 12 and 15, I and 7, and I8 and 23, are theinstantaneous polarities for the resetting half cycle of magneticamplifier MA3, for the gating half cycle of poses the effect of thecontrol signal in winding 43.

A control signal of sufiicient magnitude resets magnetic amplifier MASwhich then does not reset magnetic amplifier MAI and current flows inthe output circuit of magnetic amplifier MAI.

Magnetic amplifier MA2 may be so biased that it is cut off for allcurrents in control winding 9 less than a selected value, namely for allcurrent values present as long as the contactor ACC is open. Withmagnetic amplifier MA2 cut-oft, no feedback signal is fed to magneticamplifier MA3. When the contactor ACC closes and thus effects a higherinductance of coil 5, heavy current flows in control winding 9.

The winding relation of winding 9 with respect to windings 22 and 33 issuch that the ampere turns decrease the resetting of the core ofmagnetic amplifier MA2.

When the output of magnetic amplifier MA2 increases, due to thedecreased resetting current, current is supplied to the feedback winding42 on magnetic amplifier MAS. This current in the feedback winding 42opposes the control signal in winding 43 and increases the outputvoltage of magnetic amplifier MA3 and thus reduces the output voltage ofmagnetic amplifier MAI. The aim of protecting the coil 5 against unsafecurrent values is thus attained, while safely holding the armature A inactuated position.

When the control signal in winding 43 of magnetic amplifier MAS isremoved, the voltage output of magnetic amplifier is at full value andmagnetic amplifier MAI is substantially cut off. The contactor ACC thusdrops out.

tions and arrangements are possible all falling within the spirit andscope of our invention.

We claim as our invention:

1. In an electric system of control, in combination, an inductive loadthe energization of which is to be controlled, said inductive load inuse having a variable impedance, a magnetic amplifier having a magneticcircuit and having a main winding and two control windings, all of saidwindings being interlinked with the magnetic circuit, a rectifier, apair of terminals in use energized with single-phase alternatingcurrent, a circuit including the main winding, the rectifier, and theinductive load connected across said terminals, means for so energizingone of the control windings to effect a selected effective degree ofsaturation of the magnetic circuit to thus energize the inductive loadwith pulsating direct current of a magnitude dependent on the selectedeffective degree of saturation of the magnetic circuit and the impedanceof the inductive load, and means for energizing the second controlwinding as a function of the impedance of the inductive load todecreased the saturation of the magnetic circuit with a rise of theimpedance of the inductive load.

2. In an electric system of control, in combination, an inductive loadnormally in use having the characteristic to rapidly increase itsimpedance upon energization with alternating current but the impedanceof which rises less rapidly if energized with pulsating direct current,a magnetic amplifier in use suitably energized and having an outputcircuit for producing pulsating direct current, circuit means forconnecting the inductive load to the output circuit of the magneticamplifier, and control means responsive to the rise of impedance of theinductive load to decrease the output of the magnetic amplifier as afunction of the rise of impedance of the inductive load.

3. In a system of control, in combination, an inductive load unit in useupon energization manifesting a rise in impedance, a magnetic amplifierhaving a magnetic 0 core, a main winding on the core, and rectifierconnected to energize the load unit from a suitable source ofalternating current, a control winding for the magnetic amplifier sowound on the core to effect operation of the magnetic amplifier so as toenergize the load unit, a sec- 5 ond control winding for the magneticamplifier, said sec- Either method of precedure, as shown in Fig. 1 orFig. 50

2, however, gives a safe and efficient means of limiting the current incoil 5 after the contactor has operated. The result is that analternating-current contactor can be operated from a half move sourcewith a current limit scheme that does not require resistors andauxiliary contacts.

For some applications it is desirable to indicate the condition of thecircuit including the coil 5. The device 50 is shown interconnected withthis circuit. The device 50 may be a meter, or signal light indicatingwhether or not contactor ACC has operated. The device 50 may alsoconstitute control means for effecting operation of other circuitrydepending on the operation of contactor ACC.

While we have shown and described but two embodiments of our invention,it is apparent that other modifica-- ond control winding beinginterconnected with the load unit and so disposed on the core to effecta decrease in the magnetic amplifier output with a rise in impedance ofthe load unit.

4. he system ofcontrol, in combination, an inductive load unit in useupon energization manifesting a rise in impedance, a magnetic amplifierhaving a main winding and rectifier connected to energize the load unitfrom a suitable source of alternating current, a control winding .forthe magnetic amplifier to effect operation of the magnetic amplifier soas to effect energization of the load unit, a second control winding forthe magnetic amplifier and a second rectifier, poled in opposition tothe first rectifier, connected in series with the second controlwinding, said second control winding and second rectifier beingconnected in parallel with the load unit, the second control windingbeing so wound with respect to the other windings of the magneticamplifier to decrease the output of the magnetic amplifier with a risein impedance of the load unit.

5. In an electric system of control, in combination, an inductive loadunit in use, upon initiation of its energization, manifesting a rise inimpedance, at first magnetic amplifier having a main winding andrectifier connected in series therewith comprising the output circuit ofthe magnetic amplifier, said output circuit in use being connected to asuitable source of alternating current and being'connected to energizethe load units, said magnetic amplifier having a control winding forselecting the triggering point of the magnetic amplifier, and havljr inga second control winding for altering the output of the magneticamplifier, a second magnetic amplifier having a main winding connectedin series with a rectifier, the second control winding of the firstmagnetic amplifier and a suitable source of alternating current, saidsecond magnetic amplifier having a bias winding for selecting itstriggering point and having a second control winding and a rectifierconnected in series therewith, this second control winding and seriesconnected rectifier being connected in parallel with the load unit withthis rectifier being poled in opposition to the pol-ing of the rectifierin series with the main winding of the first magnetic amplifier.

References Cited in the file of this patent UNITED STATES PATENTS2,518,865 Cartotto Aug. 15, 1950 2,706,764 Mitchell Apr. 19, 19552,747,109 Montner May 22, 1956 2,816,260 Scorgie Dec. 10, 1957 2,849,662Britten Aug. 26, 1958

